A torque converter is a fluid-coupling device that provides smooth transition of engine power to a transmission. A stator located in the torque converter multiplies torque by altering the direction of oil flow between a pump and a turbine. This change in direction increases the inertial fluid force on the pump assembly thereby increasing turbine torque. Since the stator reroutes the fluid and is located in the center of the fluid coupling flow, it receives a high amount of thermal energy, and therefore it is considered to be the hottest element within the torque converter.
Certain protections must be programmed into the transmission control to prevent overheating. In the event of a high-temperature condition, the transmission is operated in a hot mode to protect against overheating. Three traditional methods to diagnose the hot mode include: conventional, estimated stator and predictive sump. Using the conventional method, stator temperature threshold calibrations determine the hot mode entrance and exit criteria. The estimated stator method uses calibrations controlling the amount of time a transmission can maintain a certain speed ratio without exceeding temperature targets. The predictive sump method controls hot mode entry based upon the rate of change of the sump temperature.
Although these methods are effective in preventing the transmission from overheating, each retains certain disadvantages. The conventional method may only be used for limited applications because most transmission configurations exceed stator or cooler line temperature thresholds under minimum speed ratio testing. The predictive method is overly aggressive under high heat generation conditions, is inaccurate at low speeds and does not adequately protect the transmission under Driver Shift Control functionality. The predictive sump method must have a built in safety factor to account for the delay between the heat generation and rise in sump temperature. In addition, each of the above methods require a significant amount of time and resources for calibration.